Data sensor coordination using time synchronization in a multi-bus controller area network system

ABSTRACT

A method is provided for synchronizing time in an unsynchronized vehicle controller area network system. A master control unit receives a global time from a time synchronization source. The master control unit estimates a respective time delay in transmitting messages by electronic control units on each controller area network bus. The time delay is a difference between a time when a message is generated by a respective electronic control unit for transmission on a respective controller area network bus and a time when the message is transmitted on the respective controller area network bus. The global time is adjusted for each respective controller area network bus based on the estimated time delays associated with each respective controller area network bus. Global time messages from the master control unit are transmitted to each electronic control unit that include the adjusted global times for an associated controller area network bus.

BACKGROUND OF INVENTION

An embodiment relates generally to vehicle controller area networksystems.

Controller-area network (CAN) is a vehicle bus standard intended toallow electronic control units (ECUs) and other devices to communicatewith one another without a central or host computer. Vehicle systems andsubsystems have numerous ECUs that control actuators or receive datafrom sensing devices. Many subsystems that the ECUs control areindependent subsystems having no communication with another subsystem,while other subsystems communicate and share data (e.g., engine controlunit and the electronic braking control unit).

The CAN system is an asynchronous broadcast serial bus which allowsmessages to be communicated serially. Therefore, messages between ECUswhen transmitted are not necessarily transmitted immediately over theCAN bus when a message is generated. If the CAN bus is free, the messageis instantly transmitted. If more than one message is transmitted, themore dominant message is transmitted. This is known as an arbitrationprocess. A CAN message with a highest priority will dominate thearbitration and a message transmitting at the lower priority will sensethis and wait. This is achieved through a binary bit system usingdominant bits and recessive bits. A CAN message includes an ID thatidentifies a message-type or sender. The ID consists of a predeterminednumber of data bytes. For example, an ID may consist of 8 data bytesutilizing “0”s and “1”s. Dominant bits are a logical “0” and recessivebits are a logical “1”. Dominant bits receive the higher priority thando the recessive bits. During an arbitration process, the more dominantID having the lower bit value will win arbitration and have priority.

Due to the delay in transmitting information in the recessive bits, datasharing and integration of data between two ECUs of different CAN busesin a multi-CAN bus architecture may result in out of synchronized databeing integrated together if their clocks are not synchronized. That is,to integrate data, a processor must know that it is using data that iscollected by the various sensors at substantially a same instant oftime. ECUs utilize their local clocks to time-stamp data, and if thelocal clocks are not synchronized, then a mismatch of timed data mayoccur during data integration process. A vehicle could use an internalclock in attempts to synchronize the time of all the ECU's by sendingout a clock signal; however, due to the asynchronous nature of the CANsystem and delays that result in transmitting messages across differentCAN buses, a message containing a clock signal may be delayed as well ingetting to the ECU's which would result in the local clocks of the ECUsof different CAN buses being unsynchronized. In a vehicle-to-vehicle(V2V) case, it may also be relevant for vehicles to use sensor data fromother vehicles to perform onboard sensor fusion and perform appropriateactuation and control. The sensors connected to CAN bus in remotevehicles which are transmitted using V2V messages need improved accuracythan what is available with using just the V2V time synchronizationmechanism that is typically based on GPS.

SUMMARY OF INVENTION

An advantage of an embodiment is the synchronization of local clocks inan asynchronous controller area network having a plurality controllerarea network buses which allows the coordination of data from varioussensors within a controller area network system. The delays associatedwith messages transmitted within each controller area network bus in thesystem are estimated and a global time is adjusted for each controllerarea network bus to account for the delays. Messages that include theadjusted global time for each respective controller area network bus aretransmitted to the various devices to adjust and synchronize localclocks.

An embodiment contemplates a method of synchronizing time in anunsynchronized vehicle controller area network system. The system havinga plurality of electronic control units in communication within oneanother via a plurality of controller area network buses. The electroniccontrol units are in communication with sensing devices for collectingsensed data obtained by the sensing devices. Each electronic controlunit transmits messages on the plurality of controller area networkbuses for sharing sensed data with other electronic control units (whichmay be within the vehicle in consideration or could be in anothervehicle in the case of V2V). The plurality of electronic control unitsare in communication with a master control unit via the plurality ofcontroller area network buses. The master control unit receives a globaltime from a time synchronization source. The master control unitestimates a respective time delay in transmitting messages by theelectronic control units on each controller area network bus. The timedelay is a difference between a time when a message is generated by arespective electronic control unit for transmission on a respectivecontroller area network bus and a time when the message is transmittedon the respective controller area network bus. The global time isadjusted for each respective controller area network bus based on theestimated time delays associated with each respective controller areanetwork bus. Global time messages from the master control unit in eachvehicle are transmitted to each electronic control unit that include theadjusted global times for an associated controller area network bus.Each electronic control unit connected to the controller area networkreceiving a respective global time message synchronizes a local clockbased on the adjusted global time in the respective global time message.Since a common notion of time is shared between multiple vehicles, thetime stamp taken at a given sensor on a given vehicle could betranslated to determine the time of occurrence of a sensing event on adifferent vehicle. The remote sensor data may be used as part of localsensor fusion to perform the necessary time synchronized actuation andcontrol on the vehicle.

An embodiment contemplates a vehicle communication system that includesa plurality of sensing devices for obtaining vehicle-related data. Aplurality of electronic control units receives vehicle-related data fromthe plurality of sensing devices. A plurality of controller area networkbuses coupled to the plurality of electronic control units transmits thevehicle-related data. A master control unit is in communication witheach of the plurality of controller area network buses. The mastercontrol unit estimates a respective time delay for messages transmittedon each controller area network bus. The time delay is a differencebetween a time when messages are generated for transmitting and a timewhen messages are expected to be transmitted on an associated controllerarea network bus. A time synchronization source generates a global time.The global time is adjusted by the master control unit for eachrespective controller area network bus based on the respective timedelay determined in each controller area network bus. The master controlunit transmits a respective message on each controller area network busthat includes the respective adjusted global time for each controllerarea network bus. Each electronic control unit receiving the respectivemessage synchronizes a local clock to the adjusted global time receivedin the respective message.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an architectural layout of a controller area network system.

FIG. 2 is a flowchart of a method for synchronizing time in thecontroller area network system.

FIG. 3 illustrates a flowchart of an architectural layout of acontroller area network for a V2V communication system.

DETAILED DESCRIPTION

There is shown in FIG. 1 an architectural block diagram of a vehicularcontroller area network (CAN) system 10 for synchronizing local clocksof electronic control units coupled to the network. The CAN system 10includes a plurality of CAN buses, such as a first CAN bus 12, a secondCAN bus 14, a third CAN bus 16, a fourth CAN bus 18, and a fifth CAN bus20. It should be understood that the CAN system 10 may include more orless CAN buses than shown.

Each of the CAN buses are coupled to a plurality of electronic controlunits (ECUs) 22 which allow the ECUs to communicate with one another.Each of the plurality of ECUs 22 is coupled to one or more sensors 24.The term sensors used herein is meant to include actuators and otherdevices that exchange digital signals during operation. The sensors 24are not directly connected to a respective CAN bus, but are connectedthrough the ECU. For the purposes of this invention, it is understoodthat CAN networks are known in the art and other devices such as CANcontrollers and transceivers which are typically integrated within theECU are referred to as nodes and the details of their composition willnot be discussed in detail herein. The CAN system 10 is an asynchronousbroadcast serial bus network which transmits messages serially on eachCAN bus. Therefore, any node may readily transmit a message if therespective CAN bus which it is communicating on is free. However, if twoor more nodes are transmitting messages, then a message with a moredominant ID will have priority over the messages that have less dominantID. Therefore, a message transmitted with a higher priority (i.e., moredominant ID) will always win the arbitration process and the messagewith the lesser priority (i.e., less dominant ID) will wait until theCAN bus is free or until that respective message is the most dominant IDwaiting to transmit. As a result, there are inherent delays in thetransmitting messages on the CAN-bus.

A master control unit 26 is shown in FIG. 1 that includes one or moremicroprocessors such as microprocessor 28 and microprocessor 30 that arecoupled to the plurality of CAN buses for communicating with theplurality of ECUs 22. It should be understood that more or lessmicroprocessors within the master control unit 26 may be utilized. Eachof the microprocessors within the master control unit 26 communicatesthrough a communication medium including, but not limited to, auniversal asynchronous transmitter and receiver (UART) or serialperipheral interface bus.

The master control unit 26 is a dominant ECU controlling some operationof vehicle functionality during a current time period, but may changedepending on the mode of operation of the vehicle. For example, thevehicle may utilize a wireless communication system (e.g., OnStar®) thatprovides in-vehicle security, safety, and communications service such ashands free calling, turn-by-turn navigation, and remote diagnosticssystems. Under normal vehicle operations, the OnStar® ECU may be themaster control unit 26. If vehicle-to-vehicle (V2V) communications areinitiated between the host vehicle and other remote vehicles detectedaround the host vehicle, the master control unit 26 may change to theV2V communication ECU. The master control unit 26 is used in the presentinvention to synchronize time across devices coupled to the plurality ofCAN-buses as will be described in detail later.

The CAN system 10, as shown in FIG. 1, further includes a gateway ECU 32that provides system interoperability for joining together two CAN busesthat are operating on different networks or different protocol settingsthat are not directly coupled through the master control unit 26. TheCAN buses connected through the gateway ECU 32 are disconnected in termsof their real-time behavior, so the timing of events or messages can behard to estimate even though the estimation of timing events within eachrespective CAN bus is fairly predictable.

Vehicle data from various sensors, actuators, and other devices aretypically shared between subsystems for determining or predicting avehicle operation or condition. Integration of multiple inputs fromdifferent sources provide better accuracy, availability, and reliabilityfor a respective vehicle operation. For example, in a GPS system whenGPS data is not available from a satellite source, the vehicle may relyon secondary data such as wheel speed sensor data, steering wheel anglesensor data, and yaw data to determine a vehicle position or vehicledirection. This secondary data may be supplied from differentsubsystems. As a result, it is pertinent that the data from thedifferent subsystems must be substantially sensed at the same instanceof time when integrated, otherwise the estimated output such as positionor direction could be skewed. Such skewed results may be detrimental inapplications, such as collision avoidance systems, where it is pertinentthat the integrated data used to derive a result is time-synchronized.While integration of sensor data within a respective CAN-bus isrelatively easy to synchronize and integrate, synchronization andintegration of data from different CAN-buses is difficult since thedifferent CAN-buses are typically asynchronous. That is, for a singleCAN-bus, a clock signal can be transmitted on the CAN-bus and each ofthe respective ECUs on the CAN-bus will receive the message atsubstantially a same instant of time and synchronize their local clock.Although the message may be initially delayed from being transmitted dueto high priority messages in the CAN-bus, the delay does not affect thesynchronization since all ECUs will receive the delayed message at thesame time and will be synchronizing to a same clock signal.Communication between different CAN-buses present synchronization issuesas the CAN system cannot guarantee that each ECU will receive themessage containing the synchronization time at a same instance of time.For example, in FIG. 1, ECUs within the first CAN-bus 12 and the secondCAN-bus 14 share data. Communication on the first CAN-bus 12 is open anda message may be readily transmitted on the CAN-bus 12, but the secondCAN-bus 14 has a delay. If a message containing a synchronized time issent out to all ECUs on both CAN-buses, then all ECU's on the firstCAN-bus 12 will receive the time synchronization message and adjusttheir local clocks prior to the ECUs on the second CAN-bus 14 receivingthe time synchronization message. As a result, local clocks of the ECUsof the first CAN-bus 12 will not be synchronized with the local clocksof the ECUs of the second CAN-bus 14. Any data shared between the twoECUs of the different CAN-buses may be improperly integrated due to theunsynchronized time stamping of the data. Therefore, the embodimentsdescribed herein provide a technique for synchronizing local clocksacross asynchronous CAN-buses.

The master control unit 26 as shown in FIG. 1 is directly coupled toeach CAN-bus or is indirectly coupled to a CAN-bus through one or moregateways 32. Each microprocessor 28 and 30 within the master controlunit 26 estimates a protocol stack time delay for each CAN-bus that itis directly coupled to. The protocol stack time delay is determined bythe difference in time when a message is generated for transmission by arespective ECU on a respective CAN-bus and when the message is actuallytransmitted on the respective CAN-bus. For example, microprocessor 28communicates with ECUs on the first CAN-bus 12 to retrieve informationfor determining delays. The data within the message is time-stamped whenthe respective message is actually transmitted on the first CAN-bus 12.The microprocessor 28 determines the difference between the time whendata is time-stamped by the ECU and the time when the message isactually transmitted on the CAN-bus 12. The delay may be determined bythe following formula:Delay d ₁=Transmission time(at bus)−Generation time(at source)  (1).A plurality of time-stamped data may be collected from various sensorson the CAN-bus 12 to determine an average delay time. Each delay isdetermined using the formula set forth in eq. (1). The average delay isrepresented by the following formula:Avg. Delay(Expected)=(d ₀ +d ₁ +d ₂ +d ₃ . . . +d _(n))/n.  (2)The use of high priority CAN identification will guarantee minimalvariation due to delay from bus arbitration. Moreover, when determiningthe expected delay, an option may be to remove the largest and/orsmallest delay time from the group before calculating the average delaytime.

In FIG. 1, microprocessor 28 determines the delay time for eachrespective CAN-bus that it is coupled to, specifically, the firstCAN-bus 12, the second CAN-bus 14, and the third CAN-bus 16.Microprocessor 30 determines the delays for the fifth CAN-bus 20. Thegateway ECU 32 communicates with microprocessor 28 for providing delayinformation relating not only to the protocol stack delays on the fourthCAN-bus 18, but will also provide delays relating to the processing ofdata involving the interoperability between the third CAN-bus 16 and thefourth CAN-bus 18.

After each delay is determined for each of the CAN-buses in the CANsystem 10, the master control unit 26 receives a global time from a timesynchronization source. The time synchronization source may be aninternal synchronization source 34 such as an internal clock of themaster control unit 26 or the network timing protocol (NTP). The timesynchronization source may also be an external time synchronizationsource 36 such as, but not limited to, a vehicle GPS receiver, a CDMAcell phone time signal, an atomic clock signal, a roadside unit in avehicle-to-infrastructure system, an entity in a vehicle-to-vehiclecommunication system, or the internet.

The master control unit 26 determines an adjusted global time for eachCAN-bus by adding the expected delay for a respective CAN-bus to theglobal time received by the time synchronization source. For CAN-busesthat have no delay, the adjusted global time will be the global time asreceived by the time synchronization source.

In regards to CAN-buses that are coupled to the master control unit 26through the gateway 32 such as the fourth CAN-bus 18, the message willcontain the adjusted global time, which includes both the estimatedprotocol stack time delay of the fourth CAN-bus 18 and estimated gatewaytime delay. Adjusted global times of any additional CAN-buses that arecoupled by another gateway are determined by adding the respectivegateway time delays and the protocol stack time delays.

Upon each ECU of each CAN-bus receiving their respective timesynchronization message, each ECU will synchronize their local clocksbased on the adjusted global time provided in the received message. As aresult, each ECU within the CAN system 10 will be time synchronized withone another. Data may be readily time-stamped and transferred betweenECUs of different CAN-buses for data sharing and integration.

It should be understood that the advantages of the embodiments describedherein are not isolated to a CAN system for one vehicle, but may beapplied to data sharing between a plurality of vehicles within a V2Vsystem or entities within any Vehicle-to-Any road user entity (V2X)system. The same procedure is applied to a plurality of vehicles suchthat a consensus between the vehicles or entities is made as to whatsource will be utilized as the time synchronization source. Thereafter,each vehicle determines its respective delays on each of its CAN-buses.The global time provided by the time synchronization source is thenadjusted with respect to the delays encountered in each CAN-bus of eachvehicle. The result is a plurality of participating vehicles being timesynchronized to a common time source. It should also be understood thatthe time synchronization source can be any one of the vehicles so longas all the vehicles participating agree as to which vehicle is theglobal time source. Under this procedure, the V2V ECU within eachvehicle will function as an electronic control unit and the agreed uponvehicle providing the time synchronization will function as the mastercontrol unit for the group.

FIG. 2 illustrates a method for synchronizing time within a vehicle CANsystem. In step 40, the synchronization routine is initialized. In step41, respective time delays are estimated for each CAN-bus within the CANsystem. The time delays are protocol stack delays that are thedifference between the time when the message is generated and the timewhen the message is actually transmitted.

In step 42, a determination is made as to whether any gateways arepresent between two CAN-buses. If no gateways are present, then theroutine proceeds to step 44. If gateways are present, the routineproceeds to step 43.

In step 43, a gateway time delay and the protocol stack time delay ofthe forward looking CAN-bus is determined. The gateway delay includestime delays as a result of the processing data between the twoCAN-buses, and the protocol stack time delay includes delays intransmitting messages in the forward looking CAN-bus.

In step 44, a global time is received from a time synchronizationsource.

In step 45, the global time associated with each CAN-bus is adjustedbased on the expected delays determined for each CAN-bus. Each messagetransmitted over a CAN-bus will include the adjusted global time thathas been adjusted based on the delays determined for that respectiveCAN-bus.

In step 46, messages are transmitted by the master control unit thatincludes the adjusted global time for each respective CAN-bus.

In step 47, each ECU on a respective CAN-bus adjusts their local clockto adjusted global time contained in the received message.

FIG. 3 illustrates an embodiment utilizing V2V communications betweenvehicle communication system 30 and vehicle communication system 60 ofanother vehicle. The vehicle communication system 60 includes aplurality of electronic control units (ECUs) 62 which share data withone another. Each of the plurality of ECUs 62 is coupled to one or moresensors 64. A plurality of CAN buses 66 and 68 are coupled to a mastercontrol unit 70 within the vehicle communication system 60. Under V2Vcommunications between vehicle communication system 10 and vehiclecommunication system 60, two respective electronic control units of thedifferent vehicles share data with one another.

To share the data, the local clocks of the ECUs of each vehicle must besynchronized in order to successfully combine data between the vehicles.For example, a first vehicle includes vehicle communication system 10and a second vehicle includes vehicle communication system 60. The firstvehicle is closely following the second vehicle. The first vehicle has avehicle application that provides automatic braking control based notonly on the data provided by the sensors of its own system, but may relyon data provided by the second vehicle. Communications between the firstvehicle and the second vehicle is beneficial for understanding thebraking force and speed of the second vehicle. When the second vehicleinitiates a hard brake action, one of the respective ECUs 62 from thesecond vehicle obtains the sensed braking data and speed data as aresult of the hard braking action. The braking and speed data signalfrom the second vehicle if communicated to the first vehicle could beused to actuate automatic braking of the first vehicle. To determine ifthe automatic braking is necessitated, the first vehicle must obtain itsown speed data from one of its respective ECUs 22 and analyze thebraking and speed data provided by the second vehicle. However, theintegration and analysis of the data from both vehicles will only beuseful if the data is obtained from sensors at substantially a sameinstance of time. If each of the data is not from obtained fromsubstantially a same instance of time, then the first vehicle may bemaking decisions based on data that is not current/timely.

To determine whether the data from both vehicles can be combined, themessages containing the data are time-stamped for determining therespective time when the data is obtained. Therefore, the local clocksof each vehicle communication system must be synchronized within oneanother. Utilizing the procedures described herein, the local clocks ofeach ECU of both vehicles are synchronized with one another utilizing atime synchronization source 36. Each communication system adjusts theglobal time received by the time synchronization source 36 andincorporates the expected delays of each CAN-bus. As a result, eachlocal clock in each ECU for each vehicle is synchronized. This allows arespective ECU to make a direct comparison of the obtained data todetermine if the data was sensed at substantially a same instance oftime.

While certain embodiments of the present invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention as defined by the following claims.

What is claimed is:
 1. A method for synchronizing time in anunsynchronized vehicle controller area network system, the system havinga plurality of electronic control units in communication within oneanother via a plurality of controller area network buses, the electroniccontrol units are in communication with sensing devices for collectingsensed data obtained by the sensing devices, each electronic controlunit transmitting messages on the plurality of controller area networkbuses for sharing sensed data with other electronic control units, andthe plurality of electronic control units are in communication with amaster control unit vehicle via the plurality of controller area networkbuses, the method comprising the steps of: the master control unitreceiving a global time from a time synchronization source; the mastercontrol unit estimating a respective time delay in transmitting messagesby the electronic control units in each controller area network bus, thetime delay being a difference between a time when a message is generatedby a respective electronic control unit for transmission on a respectivecontroller area network bus and a time when the message is transmittedon the respective controller area network bus; adjusting the global timefor each respective controller area network bus based on the estimatedtime delays associated with each respective controller area network bus;and transmitting global time messages from the master control unit toeach electronic control unit that include the adjusted global times foran associated controller area network bus, wherein each electroniccontrol unit connected to the controller area network receiving arespective global time message synchronizes a local clock based on theadjusted global time in the respective global time message.
 2. Themethod of claim 1 wherein the vehicle controller area network systemincludes gateways for providing system interoperability betweenadjoining controller area network buses, wherein the gateway delays areadded to the time delays and transmitted to respective electroniccontrol units succeeding the gateway.
 3. The method of claim 1 whereinsensed data obtained by a sensing device is collected by a respectiveelectronic control unit, wherein the sensed data is time-stamped by therespective electronic control unit using the synchronized local clockprior to being transmitted on the respective controller area networkbus.
 4. The method of claim 3 wherein the sensed data transmitted byelectronic control units of different controller area network buses isintegrated based on the synchronized time-stamp of the sensed data. 5.The method of claim 4 wherein a global time is transmitted to aplurality of vehicles, wherein a respective master control unit of eachvehicle determines time delays on each respective controller areanetwork bus, wherein the global time is adjusted based on the time delayof each controller area network in each vehicle, wherein the adjustedglobal times determined by each master control unit of each vehicle aretransmitted over each respective controller area network bus forsynchronizing local clocks of the electronic control units of theplurality of vehicles.
 6. The method of claim 5 wherein sensed data fromthe plurality of vehicles is wirelessly transmitted between theplurality of vehicles, wherein the sensed data from the plurality ofvehicles is integrated based on the time-stamp of the sensed data. 7.The method of claim 1 wherein the global time is obtained from a GPStime source.
 8. The method of claim 1 wherein the global time isobtained from a cell phone signal.
 9. The method of claim 1 wherein theglobal time is obtained from an atomic clock.
 10. The method of claim 1wherein the global time is obtained from an internet.
 11. The method ofclaim 1 wherein the global time is obtained from a designated vehiclewithin a group of vehicles in a vehicle-to-vehicle communication system.12. The method of claim 1 wherein the global time is obtained from aroad side equipment of a vehicle-to-infrastructure communication system.13. A vehicle communication system comprising: a plurality of sensingdevices for obtaining vehicle-related data; a plurality of electroniccontrol units for receiving vehicle-related data from the plurality ofsensing devices; a plurality of controller area network buses coupled tothe plurality of electronic control units for transmitting thevehicle-related data; a master control unit in communication with eachof the plurality of controller area network buses, the master controlunit estimating a respective time delay for messages transmitted on eachcontroller area network bus, the time delay being a difference between atime when messages are generated for transmitting and a time whenmessages are expected to be transmitted on an associated controller areanetwork bus; a time synchronization source for generating a global time;wherein the global time is adjusted by the master control unit for eachrespective controller area network bus based on the respective timedelay determined in each controller area network bus, wherein the mastercontrol unit transmits a respective message on each controller areanetwork bus that includes the respective adjusted global time for eachcontroller area network bus, and wherein each electronic control unitreceiving the respective message synchronizes a local clock to theadjusted global time received in the respective message.
 14. The systemof claim 13 wherein the time delay determined by the master control unitfor an associated controller area network bus is based on an averagedelay that is a function of a predetermined number of messages generatedand transmitted on the associated controller area network bus.
 15. Thesystem of claim 13 wherein the time synchronization source is anin-vehicle time synchronization source.
 16. The system of claim 13wherein the time synchronization source is an external timesynchronization source.
 17. The system of claim 16 wherein external timesynchronization source is provided through a vehicle-to-vehiclecommunication network.
 18. The system of claim 16 wherein external timesynchronization source is provided through vehicle-to-infrastructurecommunication network.
 19. The system of claim 16 wherein external timesynchronization source is a cellular phone communication service. 20.The system of claim 16 further comprising a gateway coupled to thecontroller area network buses, wherein the gateway provides systeminteroperability between two adjoining controller area network buses,wherein the gateway communicates to the master control unit time delaydata relating to time delays of messages being processed through thegateway, wherein the master control unit adds the time delay of thegateway to the adjusted global time, and wherein the adjusted globaltime that includes the time delay of the gateway is transmitted on toelectronic control units succeeding the gateway for local clocksynchronization.